1. Field of the Invention
The invention relates to a current detection circuit detecting a current flowing through a transistor and a semiconductor integrated circuit.
2. Description of the Related Art
Conventionally, a current detection circuit is sometimes built in a semiconductor integrated circuit so as to detect a current flowing through a transistor formed therein.
FIG. 6 is a circuit diagram of a current detection circuit of a MOS transistor 50. As shown in the figure, this current detection circuit is so configured that one end of a resistor 51 is connected to the source S of the MOS transistor 50, the other end of the resistor 51 is grounded, and both the ends of the resistor 51 are connected to a voltmeter 52.
In the current detection, in the state where the MOS transistor 50 is turned on by applying a gate potential at a threshold or more to the gate G of the MOS transistor 50, a drain voltage is applied to the drain D to flow a current I through the MOS transistor 50. In this case, when the resistance value of the voltmeter 52 is higher enough than the resistance value R of the resistor 51, the current I flowing through the MOS transistor 50 and the resistor 51 is almost constant. Therefore, a voltage V occurring at both the ends of the resistor 51 is measured by the voltmeter 52 to detect the current I flowing through the MOS transistor 50 by the Ohm's law (I=V/R). A relevant technique is disclosed in the Japanese Patent Application Publication No. Hei 6-58981.
However, since the potential of the source S of the MOS transistor 50 increases from the ground potential by the voltage V due to the current I flowing through the resistor 51, the current I of the MOS transistor 50 decreases. In other words, there occurs a problem that the resistor 51 of the current detection circuit influences the current flowing through the MOS transistor 50.
Furthermore, since the current I flows through the resistor 51, a power loss (W=I2R) by Joule heat occurs. In this case, when the resistor 51 of which the resistance value R is low is formed in the semiconductor integrated circuit so as to minimize the power loss, a large pattern area is needed. In particular, in the case of a power MOS transistor, the current I is significantly high and thus the problem described above is serious.